An Instrument Landing System (ILS) approach is traditionally one of the safest, most accurate precision approach systems. However, there may be occasions when the ILS is out of calibration due to various lack of maintenance, testing, or other reasons. When the ILS is not calibrated or not functioning properly, the glideslope indicator in an aircraft cockpit may indicate that the aircraft is on glideslope when the aircraft is actually below the actual and safe glideslope. The aircraft can fly into the ground if this situation continues.
Therefore, there exists a need to perform some form of back-up check to ensure the ILS is performing properly.
The present invention includes a system, method, and computer program product for alerting an aircraft flight crew of an inconsistency during an instrument landing system (ILS) approach to a selected runway. The system includes a component configured to receive glideslope and localizer signals, and a component configured to determine aircraft approach angle to runway end. Also, a component configured to alert the aircraft flight crew of an approach inconsistency, if the determined aircraft approach angle to runway end is less than a threshold angular value and one or more parameters based on aircraft position and the received glideslope and localizer signals are met.
In accordance with further aspects of the invention, the component configured to determine aircraft approach angle to runway end determines the aircraft approach angle to runway end based on aircraft geometric altitude, a vertical figure of merit, a horizontal figure of merit, runway elevation, and aircraft distance to runway threshold.
In accordance with other aspects of the invention, the parameters include valid glideslope and localizer signals, the aircraft being on the front course of the ILS approach, the aircraft being within a distance range from the selected runway based on distance to selected runway threshold, horizontal figure of merit, and a runway quality factor, the aircraft being within an angular range from the selected runway based on aircraft true track and selected runway bearing, the aircraft being below a height above runway altitude value based on geometric altitude, a vertical figure of merit, and runway elevation, and the received glideslope and localizer signals indicating that the aircraft is within threshold values of center of the ILS approach.
As will be readily appreciated from the foregoing summary, the invention provides an improved ILS that performs an on-aircraft check if the aircraft is receiving an incorrect indication of being on or nearly on glideslope while the aircraft is actually dangerously below glideslope.